Method for overcoming embrittlement of steel alloys



METHOD FOR OVERCOMING EMBRITTLEMEN OF STEEL ALLOYS Leroy E. Fink,Beaverton, reg., assignor, by mes ne assignments, to Electric SteelFoundry Company, a corporation of Oregon No Drawing. ApplicationDecember 24, 1954,

Serial No. 477,576

4 Claims. (Cl. 75130) This invention relates to a method for overcomingembrittlement of steel alloys, and is particularly useful in combattingthe embrittlement or cracking tendency known as hot shortness in lowcarbon corrosion-resistant austenitic stainless cast steels.

In the manufacture of low carbon corrosion-resistant austeniticstainless steels, it is found that the alloy is difiicult to cast, weld,or hot work, without the tendency to be hot short. Hot shortness may bedefined as a brittleness which occurs in the metal when hot, the metalseparating in most cases at the grain boundary. In the castingoperation, as the casting cools from the liquid state to the solid statein the mold, the mold sets up a restric tion to the contracting metal.Many steels and alloys are strong enough to resist this restriction, butconsiderable difliculty is found with austenitic stainless steels, andtearing occurs in the casting, which must be welded. Welding alsobecomes a problem, since the metal adjacent the weld is heated, andfrequently cracking will occur in this adjoining portion, requiringcontinual repairs, and eventually the product must be scrapped.

I have discovered that such austenitic stainless steel alloys may beeffectively treated to prevent hot shortness by adding to the alloywhile molten a compound of vanadium, titanium and boron. I prefer to addthe vanadium and titanium as ferro-compounds, and I find it desirable toemploy the vanadium and titanium as a. combined ferro-compound.

The combination of vanadium, titanium and boron may be added to themolten alloy while in the furnace, as, for example, in an are orinduction electric furnace, just before tapping. If desired, it may beadded to the ladle during tapping.

The proportions of the compounds are preferably employed within certainlimits which are effective in producing the best results. For example,the vanadium is preferably used in the proportion of 0.02% to 1.07%, thetitanium in the proportion of 0.01% to 0.6%, while the boron is added ina very small amount, ranging from a trace to 0.002%. I have found thatbest results are obtained when the vanadium is used in the range of0.05% to 0.25%, the titanium in the range of 0.01% to 0.15%, and theboron in about 0.002%.

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2 treated in accordance with the present invention disclose very few, ifany, perceptible cracks. I In the operation of the process, theaustenitic stainless steel alloy is brought to a molten condition withinthe furnace and the ferro compound of vanadium and titanium and theboron are added to the metal in the furnace or,

if desired, to the ladle during tapping. Aluminum may be added in thedioxidizing procedure, in accordance with general furnace practice, andsilicon may also be added for the maintenance of the physical propertiesand to promote fluidity. If desired, the aluminum and silicon may beadded simultaneously with the titanium, vanadium and boron, and theproportions of these will be the proportions usually added according togeneral furnace practice. Specific examples of the process may be setout as follows:

Example I A stainless steel alloy having the following analysis:

Percent Carbon rnax 0.07 Manganese 2.00 Silicon max- 1.5 Chromium 20.5Nickel 29.3 Molybdenum 2.4 Copper Q. 3.3

The operation Was carried on as described in Example I, except that thevanadium was in the proportion of 0.25%, the titanium in the proportionof 0.15%, the

. boron remaining at about 0.002%. The results obtained In general, thevanadium employed is about twice that of the titanium, although I findthat best results are obtained when the titanium is about three-fifthsof the vanadium. I find that all three materials, namely, the vanadium,titanium and boron, cooperate in eliminating the hot shortness, and whenused in the percentages shown, the finished tested product showspractically no cracks even after the flame test and Zyglo inspection. Inthe test generally referred to as the flame test, one end of thespecimen is subjected to a torch for one minute, and thereafter a greenfluorescent penetrant dye is applied and developed so as to disclose thepresence of minute cracks, etc. Since such tests are well known, adetailed description herein is believed unnecessary and it is sufiicientto say that under such rigorous tests the products were comparable tothose described in Example I.

Example III The process was carried out as described in Example I exceptthat the austenitic stainless steel had a different composition,containing 24% chromium, 20.5% nickel, 0.08% carbon, about 1.5%manganese, and 1.0% silicon. The procedure as described in Example I wasfound to eliminate hot shortness in the above-described alloy.

Example IV The process was carried out as described in Example I,

except that the stainless steel alloy treated had about 17.65% chromiumcontent, 13.65% nickel, 2.65% molybdenum, 0.08% carbon maximum, about1.25% manganese, and about 1.0% silicon. Hot shortness Was eliminated bythe adding of the materials described in Example I.

Example V The process was carried out as described in Example IV, exceptthat the stainless steel alloy treated had about 18.7% chromium and10.5% nickel, the carbon, manga nese, and silicon contents being thesame as shown in Example IV. Comparable results were obtained.

Example VI The process was carried out as described in Example IV exceptthat the stainless steel alloy, which was otherwisethe same, hadachromium content of 15% and a v The same results asdescribed innickelcontentof- 35%. Example IV were obtained.

In the treatment of low carbon, corrosion-resistant aust'enitic caststainless steels, the three added material's, namely, vanadium, titaniumand boron, appear to produce together, as a total effect, theelimination of the hot shortness, and while the proportions of thesemaybe varied within a substantially Wide range depending upon the analysisof the particular austenitic cast stainless steel material beingtreated, the important new result of eliminating hot shortness isachieved by the use of all three materials.

While in the foregoing description I' have set forth in detail specificsteps and proportions for the. purpose of illustrating preferredembodiments ofthe invention, it will be understood that such details ofprocedure, proportions, etc., may be varied widely by those skilled inthe. art without departing from the spirit of my invention. I' claim:

1. In a process for preventing hot shortness in a low carbon,corrosion-resistant austenitic cast stainless steel alloy, the-stepsofheating the alloy to a molten state and 4 i then adding theretovanadium, titanium and boron in the proportions. of .05 tov 25%..vanadium, .01 to..15%. titanium, and about 002% boron.

2. The process of claim 1, in which the vanadium and titanium arecombined in a ferro-compound.

3. In a process for treating; a low-carbon, corrosionresistantaustenitic cast stainless steel alloy to prevent hot shortness thereinwhile effecting a minimum change in the alloy, the steps of heating thealloy to a molten condition and thereafter adding to the molten mass aterm-compound of vanadium, titanium and boron in proportionssubstantially less than 5% of thetotalt alloy, the vanadium, being from.05 to .25 the titanium being from .01 to .15%, and the boron being froma trace to .002%.

4. The process of claim 3, 'm which the vanadium, titanium and boron areadded to the ladle during tapping.

References Cited in the file of this patent UNITED STATES PATENTS2,432,618 Franks et a1. Dec. 16, 1.947- 2,587,613 Payson Mar. 4, 195;2,602,928 Urban July 1, 1952

1. IN A PROCESS FOR PREVENTING "HOT SHORTNESS" IN A LOW CARBON,CORROSION-RESISTANT AUSTENITIC CAST STAINLESS STEEL ALLOY, THE STEPS OFHEATING THE ALLOY TO A MOLTEN STATE AND THEN ADDING THERETO VANADIUM,TITANIUM AND BORON IN THE PROPORTIONS OF .05 TO .25% VANADIUM, .01 TO.15% TITANIUM, AND ABOUT .002% BORON.